Intrinsic electronic superconducting phases at 60 K and 90 K in double-layer YBa$_2$Cu$_3$O$_{6+\delta}$

TL;DR

This study reveals intrinsic electronic superconducting phases at 60 K and 90 K in double-layer YBa₂Cu₃O₆+δ, showing that $T_c$ depends on electronic phases related to specific doping levels, following a universal behavior.

Contribution

It identifies intrinsic electronic superconducting phases at specific doping levels and links $T_c$ behavior to electronic phases and hierarchical doping order in YBa₂Cu₃O₆+δ.

Findings

Superconducting phases at 60 K and 90 K are intrinsic and doping-dependent.

$T_c$ follows a universal curve based on planar hole doping $P_{pl}$.

Superconductivity is governed by electronic phases at hierarchical doping levels.

Abstract

We study superconducting transition temperature ($T_c$) of oxygen-doped double-layer high-temperature superconductors YBa$_2$Cu$_3$O$_{6+\delta}$ (0 $\le$ $\delta$ $\le$ 1) as a function of the oxygen dopant concentration ($\delta$) and planar hole-doping concentration ($P_{pl}$). We find that $T_c$, while clearly influenced by the development of the chain ordering as seen in the $T_c$ $vs.$ $\delta$ plot, lies on a universal curve originating at the critical hole concentration ($P_c$) = 1/16 in the $T_c$ $vs.$ $P_{pl}$ plot. Our analysis suggests that the universal behavior of $T_c$($P_{pl}$) can be understood in terms of the competition and collaboration of chemical-phases and electronic-phases that exist in the system. We conclude that the global superconductivity behavior of YBa$_2$Cu$_3$O$_{6+\delta}$ as a function of doping is electronically driven and dictated by pristine electronic phases at magic doping numbers that follow the hierarchical order based on $P_c$, such as 2 $\times$ $P_c$, 3 $\times$ $P_c$ and 4 $\times$ $P_c$. We find that there are at least two intrinsic electronic superconducting phases of $T_c$ = 60 K at 2 $\times$ $P_c$ = 1/8 and $T_c$ = 90 K at 3 $\times$ $P_c$ = 3/16.